1. Field of the Invention
The present invention relates to a process for producing a magnetic recording medium, particularly a magnetic recording medium having a magnetic layer of a continuous thin film type, by a so-called oblique vapor deposition method.
2. Description of the Prior Art
In order to attain compact winding of video and audio recording tapes, there have been active researches to develop a magnetic recording medium having a magnetic layer of a continuous thin film type.
As a magnetic layer for such a continuous thin film type medium, a vapor deposited magnetic layer composed of columnar crystal particles of e.g. Co, Co-Ni, Co-Cr or Co-Ni-Cr is most suitable from a view-point of the desired characteristics, which is formed by a so-called oblique vapor deposition method in which the vapor deposition is conducted at a predetermined inclined angle relative to the normal line of the substrate.
Further, by conducting the vapor deposition while supplying a substantial amount of oxygen to the atmosphere for the oblique vapor deposition, it is possible to cover the surface of the columnar crystal particles with an oxide layer (e.g. Japanese Examined Patent Publication No. 23208/1981), whereby the electromagnetic conversion characteristics as well as the running durability will be improved and thus better results can be expected. However, in the case of a Co-Ni system, if the oxygen supply rate is increased to increase the oxide layer, the coercive force which is an important characteristic for a high density recording medium, tends to decrease while the running durability will be improved. In order to increase the oxygen supply rate and yet to maintain the coercive force at a certain acceptable level, it is necessary to increase the angle of incidence for the oblique vapor deposition, relative to the normal line of the substrate. However, in such a case, the vapor deposition efficiency will sharply drop, and the operation will be uneconomical. Further, the film density will decrease and the corrosion resistance will be poor. Furthermore, there will be problem that due to the oxygen supplied in a great amount, the molten metal in the crucible is likely to be oxidized or a trouble in the vacuum system is likely to be led.
Thus, the recording media prepared by the conventional oblique vapor deposition method, do not fully satisfy the requirements for adequate electromagnetic conversion characteristics, running durability, economy for the production and corrosion resistance.